DESCRIPTION: Treatment of degenerative joint diseases for structural and functional restoration of cartilage remains a significant challenge. Tissue engineered cartilage with biomaterial based synthetic matrices offer a promising approach, but current biomaterials have shown limited ability for regeneration as these materials cannot mimic the mechanomorphological character of native cartilage matrix which exhibits viscoelastic and poroelastic responses. We hypothesize that these time-dependent relaxations of matrix should be mimicked in a synthetic matrix to modulate differentiation of mesenchymal stem cells into cartilage producing cells. To achieve this, our approach is to engineer amphiphilic polyurethanes as colloidal microgel which exhibits hierarchical microstructures to regulate viscoelasticity and poroelasticity in mutually exclusive manner and use these gels for chondrogenesis of mesenchymal stem cells. Amphiphilic polyurethanes can be engineered to form colloidal dispersion in aqueous medium which can be subsequently aggregated into gel under shear mode or quiescent (gravity) state. Segmental composition of amphiphilic polyurethanes can modulate viscoelastic response through relaxation of macromolecular chains of polymeric network and microstructure of colloidal gels modulates poroelastic diffusion through migration of solvent molecules. Viscoelasticity of colloidal gel matrix can modulate cell-matrix interactions while poroelastic effect can regulate cell-cell interactions during chondrogenesis of mesenchymal stem cells. Our goal is to design colloidal polyurethane gels where these two responses are tuned independently and assess the effect of matrix viscoelasticity and poroelasticity for chondrogenic differentiation. Furthermore, these stem cell seeded colloidal gels should exhibit shear- dependent self-healing character for minimally invasive transplantation as injectable gels. Through this application, we specifically propose to: (a) characterize the viscoelastic and poroelastic character of colloidal gels developed under shear induced and quiescent state from polyethylene glycol based amphiphilic polyurethanes and (b) analyze the chondrogenesis of mesenchymal stem cells within these gels to correlate the matrix relaxation effect with the differentiability of stem cells. Our long term goal is to establish polyurethane based colloidal gels as a tissue-engineered construct for cartilage defects and examine the efficacy of this approach through in vivo cartilage defect animal models. This proposed study presents a significant advancement in biomaterial based cartilage regeneration strategy and will present a therapeutically viable treatment option for arthritic cartilage.